Rolled fingerprint images are obtained by rolling a finger from one side to the other (“from nail to nail”) in order to capture a substantial area of a finger. Since rolling a finger can introduce distortion, rolled fingerprints are usually acquired in an attended mode. Rolling speed and pressure during the rolling can cause distortion on scanned fingerprint images. Plain fingerprint images are those in which the finger is pressed down on a flat surface but not rolled. Using the same rolled finger scanning device, multiple plain impressions can be taken simultaneously without rolling. These are referred to as plain, slap, or flat impressions. While a plain impression covers a smaller area than rolled fingerprint, they typically do not have the distortion introduced during rolling. In conventional fingerprint scanning devices, an operator or user is typically instructed to roll a finger in one direction from nail to nail.
It is desirable to have an efficient fingerprint enrollment apparatus that can address the deficiencies of conventional fingerprint scanning devices and also handle various rolling scenarios including, 1) rolling left to right; 2) rolling right to left; 3) start rolling near the center of the sensing surface of a fingerprint enrollment apparatus, then rolls first to the left and then to the right; 4) start rolling near the center of the sensing surface of a fingerprint enrollment apparatus, then rolls first to the right and then to the left; and 5) processing randomly selected multiple fingers simultaneously.